The present invention describes subject matter that relates to nanotechnology systems and methods that provide rapid decontamination and protection.
Huge amounts of environmental toxins, such as toxic industrial chemicals (TICs), toxic organic dyes, bio-pharmaceuticals, and chemical warfare agents (CWAs), bio-accumulate causing chronic and aesthetic pollution to the surrounding environments and human beings. Nanotechnology can provide novel systems for rapid decontamination and protection through a self-cleaning mechanism. The basic principle of this self-cleaning system is the application of photocatalysis. Nanofibrous photocatalysts use incident irradiation in the UV or visible region of the spectrum to excite an electron from the valence band (leaving behind a hole) to the conduction band of a semiconductor. These photoinduced charge carriers then proceed to form reactive radicals, hydroxyl radicals and super oxide radicals that attack adsorbed chemicals on the surface of the material. Electromagnetic radiation in the form of visible light, ultra-violet light, or even sunlight can be used to achieve enhanced photodegradation that are both rapid and inexpensive compared to the current decomposition techniques that are costly and time consuming. Metal oxide nanofibrous materials represent an alternative approach to conventional composites used in photocatalytic degradation. Their one dimensional morphology is desired compared to traditional nanoparticles; owing to excellent mobility of charge carriers, high surface area to volume ratio, the existence of pores enhancing charge collection and transport.
Metal oxide photocatalysts have been regarded as one of the most active areas in heterogeneous catalysis due to their great catalytic abilities for removing environmental pollutants relating to waste water, polluted air, and chemical warfare agents. Compared with other photocatalytic materials, one-dimensional metal oxide nanofibrous materials are particularly attractive due to their high specific surface area, ease of fabrication and functionalization, and versatility in controlling the fiber diameters and morphologies.
The prior art has taught techniques for decontamination of toxic industrial chemicals and chemical warfare agents on building materials using chlorine dioxide fumigant and liquid oxidant technologies.
Many pharmaceutical and medical facility waste streams are considered hazardous and toxic. Hospitals, nursing homes, private clinics, and laboratories are a growing source of this type of environmental pollution [1-3]. Residual and waste drugs are discarded into environmental waters through sewers with human waste or direct disposal causing serious contamination. A number of conventional techniques, such as dilution and incineration [4], are widely used to minimize the impact, however they still cannot be removed from contaminated water efficiently. Advances in the field of chemistry have resulted in many improved methods for environmental cleanup. One main focus of study has been using photocatalysts to degrade environmental pollutants [5-9].
In 1972, Akira Fujishima and Kenichi Honda first reported that titanium dioxide had a photocatalytic activity [10]. Since the initial discovery, TiO2 has become regarded as an efficient photocatalyst for degradation of organic pollutants from water due to its strong oxidative power, high stability, low cost and environmental friendliness [11-18]. The three polymorphs of TiO2, anatase, rutile and brookite, show very different photocatalytic activities. The photocatalytic activity of TiO2 is related to several different factors including degree of crystallinity, specific surface area, porosity, and crystal size [19-23]. The anatase phase of TiO2 exhibits maximum photocatalytic activity due to its higher adsorption affinity for organic molecules [21] and lower electron-hole recombination rate [25-28].
The most commonly used commercial TiO2 photocatalyst is a nanopowder, which consists of ˜25 wt % rutile and 75 wt % anatase. This Degussa P25, shows improved photocatalytic activity over pure anatase or rutile nanopowder. The synergistic effect between the three different TiO2 phases has been widely reported. Zachariah et al. [22] demonstrated that the photocatalytic activity of mixed-phase TiO2 nanoparticles was a function of rutile content with the maximum photocatalytic activity observed for 40 wt % rutile. Su et al. [29] also investigated the influence of the anatase-to-rutile ratios on their photoreactivities. A TiO2 film with ˜60 wt % anatase and ˜40 wt % rutile exhibited optimal performance and a 50% improved activity compared with pure anatase. However, Pal et al. [30] observed that TiO2 microspheres prepared by spray drying and calcined at 400° C. with 52.2 wt % of rutile phase achieved the best photocatalytic efficiency for degradation of dyes. Boppella et al. [31] found that mixed-phase TiO2 nanoparticles composing 83 wt % brookite and 17 wt % rutile exhibited superior photoactivity compared to Degussa P25 and phase-pure anatase nanocrystals. It is clear that the TiO2 phase compositions and the ratios are the key factors in optimizing photodegradation.
Compared with TiO2 nanoparticles, one dimensional TiO2 nanofibers have attracted considerable attention in recent years for energy applications [32, 33] due to their higher surface-to-volume ratio [34], faster electron diffusion to the surface [35, 36] and improved light absorption through the light scattering within the porous structure [34].
See, U.S. Pat. Nos. 8,956,910; 8,940,244; 8,932,346; 8,921,473; 8,920,491; 8,906,814; 8,900,610; 8,900,292; 8,884,507; 8,864,341; 8,840,863; 8,827,192; 8,815,275; 8,815,273; 8,771,343; 8,721,923; 8,715,855; 8,685,424; 8,684,189; 8,652,229; 8,613,363; 8,585,753; 8,574,615; 8,562,895; 8,540,826; 8,460,790; 8,460,547; 8,449,603; 8,431,149; 8,415,267; 8,414,806; 8,383,539; 8,353,949; 8,329,091; 8,318,126; 8,287,937; 8,263,029; 8,231,980; 8,225,641; 8,221,822; 8,216,961; 8,216,632; 8,197,890; 8,187,620; 8,080,335; 8,071,156; 8,070,797; 8,067,054; 8,066,763; 8,029,554; 8,002,823; 7,981,150; 7,976,915; 7,942,926; 7,938,855; 7,931,683; 7,789,930; 7,718,112; 7,709,597; 7,709,088; 7,655,112; 7,635,518; 7,575,707; each of which is expressly incorporated herein by reference in its entirety.
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